<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>太极图</title>
</head>
<style>
    * {
        margin: 0;
        padding: 0;
    }

    body {
        background-color: #CCCCCC;
    }
    div {
        margin: 100px auto;  
        width: 200px;
        height: 400px;
        background-color: #fff;
        border-left: 200px solid #000;
        border-radius: 50%;
    }

    div::before {
        display: block;
        content: '';
        width: 50px;
        height: 50px;
        background-color: #fff;
        border-radius: 50%;
        margin-left: -100px;
        /* position: relative; */
        border:75px solid #000;
    }

    div::after {
        display: block;
        content: '';
        width: 50px;
        height: 50px;
        background-color: #000;
        border-radius: 50%;
        margin-left: -100px;
        /* position: relative; */
        border:75px solid #fff;    
}
</style>

<body>
    <div></div>
</body>

</html>